FIG. 12 is a perspective view of a multiple layer semiconductor circuit module that may be an MMIC and that has been previously disclosed. The module includes a semiconductor substrate 1 made, for example, of gallium arsenide, silicon, indium phosphide, or another semiconductor material. The substrate 1 includes opposed first and second surfaces. A first semiconductor circuit 4 is disposed on and/or in the first surface of the substrate 1. The first circuit 4, preferably an active integrated circuit, may, for example, be an amplifier, a phase shifter, a switch, an oscillator, or the like. One or more of the circuits in the module may also be a passive circuit. A first electrically insulating layer 2, for example, a layer of SiON or SiN, is disposed on the first surface of the substrate 1, covering the first circuit 4. The first insulating layer 2 has side walls generally continuous with the side walls of the substrate 1. A second circuit 5 is disposed on the first insulating layer 2 opposite from and spaced from the first circuit 4 by the first insulating layer 2. The second circuit 4 may be formed on or placed on the first insulating film 2 and, for example, include thin films directly deposited on the first insulating film 2. Alternatively, the second circuit 5 may be a separately prepared integrated circuit that is mounted on the first insulating layer 2.
A second electrically insulating layer 3 is disposed on the first insulating layer 2 covering the second circuit 5. A third circuit 6 is disposed on a surface of the second insulating layer 3 opposite the second circuit 5 and spaced from the second circuit 5 by the second insulating layer 3. The second insulating layer 3 also includes side walls that are generally continuous with the side walls of the first insulating layer 2 and the substrate 1. The third circuit 6 may be formed in the same way as circuit 5, i.e., by depositing thin films directly on the second insulating layer 3 or by mounting a separately prepared integrated circuit. One or both of the second and third circuits 5 and 6, like the first circuit 4, may be selected from active circuits, such as amplifiers, phase shifters, switches, oscillators, and other circuits, or from passive circuits.
The circuits 4, 5, and 6 are electrically interconnected through via hole structures that penetrate the respective first and second insulating layers 2 and 3. For example, as shown in FIG. 12, a first via hole structure 12 electrically interconnects the first circuit 4 with the second circuit 5. As well known in the art, via hole structures include a passage extending through an insulating material. The walls of the passage are plated with, or the entire passage is filled with, an electrical conductor providing a conducting path between elements located on opposite sides of the via hole structure. In FIG. 12, a second via hole 13 provides an electrical interconnection between second circuit 5 and the third circuit 6. Via hole structures 12 and 13 are merely illustrative and the multiple interconnections between the circuits 4, 5, and 6 may be provided through the use of multiple via hole structures.
The outermost surface of the module includes a conducting strip with input and output terminals 34 and 35. When the module is an MMIC, the dimensions and the arrangement of the conductors of the input and output lines and terminals 34 and 35 are chosen to produce the best performance for the frequency range employed. In many modules, particularly those employed in a microwave frequency range, it is preferable to include a grounding electrode 25 on the second surface of the substrate 1 as shown in FIG. 12. In that case, a third via hole structure 26 extending through the substrate 1 provides a ground connection to the first circuit 4 from the grounding electrode 25.
In operation, each of the circuits 4, 5, and 6 responds to the signal applied to the input and output terminals 34 and 35 because of the interconnections provided by the via hole structures. The frequency response characteristics of the module can be determined by applying probes 19 to each of the input and output terminals 34 and 35 to supply test signals to and sense output signals from the circuits 4, 5, and 6 as shown in FIG. 13. Generally, the probes 19 are part of a transmission line, for example, a coplanar waveguide or a slot line.
Two multiple layer semiconductor circuit modules 31 and 32, of the type shown in FIGS. 12 and 13, can be interconnected as illustrated in FIG. 14. As shown there, the multiple layer semiconductor circuit modules 31 and 32 are commonly mounted on an electrically conducting base 22 with a solder 23. The solder and base electrically interconnect the respective ground electrodes 25 of the MMICs 31 and 32. Adjacent input and output terminals 34 and 35 of the MMIC 31 and MMIC 32 are interconnected by a gold ribbon or gold wire 24. Additional modules can be interconnected in the same manner as shown in FIG. 14.
In the prior art multiple layer semiconductor circuit modules of FIGS. 12-14, certain problems have arisen. For example, the via hole structures include a metal having a coefficient of thermal expansion significantly different from the coefficient of thermal expansion of the first and second insulating layers 2 and 3 and the substrate 1. When the temperature of the module changes, stresses between the via hole structure and the insulating layers and substrate are produced because of the different amounts of expansion of the different materials. These stresses can, under severe circumstances, lead to cracking of the insulating layers.
When several of the modules are interconnected, they must be interconnected through the terminals 34 and 35 which employ the via hole structures to reach circuits 4 and 5. In other words, it is not possible to connect the respective first and second circuits of the two modules 31 and 32. In addition, when a gold wire or ribbon 24 is employed to interconnect two or more of the modules, it is difficult to maintain the particular characteristic impedance of the conductor structure on the exposed surface of the modules. When the modules are used at high frequencies, for example, in a microwave range, the failure to maintain a constant characteristic impedance results in a high voltage standing wave ratio (VSWR) i.e., signal losses, and other undesirable effects.
In the module shown in FIG. 12, a direct grounding connection is made between the grounding electrode 25 and the first circuit 4 by the via hole structure 26. However, the ground connection to the second and third circuits 5 and 6 must pass through via hole structures 12 and 13, respectively, from the grounding electrode 25. Because the via hole structures have a relatively small diameter, for example, several hundred microns at most, the grounding interconnection is relatively long in relation to its cross-sectional area. At microwave frequencies, such an interconnection has a relatively large parasitic inductive component that adversely affects the operation of the circuits, for example, reducing the gain of an amplifier, altering the frequency of an oscillator, changing the threshold of a switch, altering the phase delay of a phase shifter, and the like.
The interconnections between the input and output terminals 34 and 35 and the first and second circuits 4 and 5 prevent direct measurement of the individual characteristics of the first and second circuits 4 and 5. Since the third circuit 6 is directly connected to the input and output terminals 34 and 35, the third circuit 6 influences the measurement of the characteristics of the first and second circuits 4 and 5. Likewise, the second circuit 5 influences measurements of the characteristics of the first circuit 4.